1. Field of the Invention
This invention relates to a process for reforming naphtha in a two-stage process. More particularly, the invention is concerned with a process in which in the first two stages a highly chlorinated alumina catalyst containing a metal of the platinum group is used, and in the second stage the effluent is reformed in the presence of a platinum containing reforming catalyst
2. Discussion of the Prior Art
The term "reforming" is well known in the petroleum industry and refers to the treatment of gasoline or fractions thereof to improve their anti-knock characteristics. The reforming process involves many reactions not all of which are entirely understood or even known. The primary known reactions comprise controlled or selective cracking and aromatization, the latter including dehydrogenation of naphthenic hydrocarbons to aromatics and the cyclization of straight chain or mildly branched chain aliphatic hydrocarbons of at least six carbon atoms to form aromatics. Other reactions occurring during reforming include isomerization, both of aliphatic hydrocarbons and of naphthenic hydrocarbons containing 5 and 6 carbon atoms in the ring, hydrogen transfer reactions, alkyl transfer reactions, and the like.
In the reforming process of naphthenic compounds, both cyclohexanes and cyclopentanes are converted to aromatic compounds to obtain high octane reformate. In reforming, the cyclohexanes can be converted to aromatics via simple, clean dehydrogenation reactions, while the cyclopentanes have to be first isomerized then dehydrogenated to yield aromatics. In comparison with cyclohexanes, reactions of cyclopentanes to aromatics are not only slower, but also lead to undesirable side reactions, as for example, cracking to light gases, resulting in lower reformate yield and poorer process performance.
The catalysts used in the practice of both stages (1) and (2) of this invention are generally known, as are methods of making them (see U.S. Pat. Nos. 3,218,267, 3,440,178 and 3,242,228).
U.S. Pat. No. 3,849,289 teaches a staged reforming process comprising charging a naphtha to a first reaction zone and contacting the naphtha with hydrogen in the presence of a reforming catalyst and charging the effluent to a second reforming zone. The temperature in the first zone is from about 750.degree. F. to about 850.degree. F., and the catalyst used is the conventional platinum-alumina reforming catalyst. The distinguishing feature of the invention is the discovery of the effect of catalyst particle size in optimizing the reaction. Furthermore, although it is known that certain platinum-alumina catalysts can be used at lower temperatures (U.S. Pat. No. 3,218,267, for example, teaches the use of temperatures as low as 400.degree. F.) no patent or combination of patents suggests the process of the instant invention.